Lightweight materials with adequate mechanical properties are highly desired for various structural applications. It is speculated that in the near future every structure, simple or complex, will be fabricated using 3D printing technology. Various materials being explored for 3D printing are laser sintered metals, photo-crosslinked polymers and extruded molten polymers. However, all these materials have inherently high densities which render them unsuitable for lightweight structures.
Silica aerogels are highly porous materials, composed of over 90% air and the rest as silica network structure. This unique composition and structure impart peculiar properties such as high surface area, very low bulk density and low thermal conductivity. They find applications in at least catalysis,1,2 adsorption,3 thermal insulation,4,5 environmental remediation6 and space exploration.7 
Aerogels are not generally seen as a structural material for a number of reasons. They are fragile, synthesis requires several steps, and drying is complex and time-consuming.
Aerogel fragility issues have been addressed in large part by the Leventis group,8,9 who crosslinked the skeletal oxide nanoparticles with a conformal polymer coating. Crosslinking increases mechanical strength by orders of magnitude without overly compromising porosity. The strengthening strategies include use of higher functionality cross-linker, selective crosslinking of the regions subject to shear and mechanical stress, and specific patterning like honeycomb structures to increase compressive strength of aerogels along the load-bearing direction.10-12 
Drying is another issue affecting aerogel applications. To reduce capillary forces (which cause cracking during drying), supercritical CO2 is typically employed. However, supercritical CO2 drying requires multiple, time-consuming solvent exchanges, which make the method impractical for large-scale applications. Drying issues have been partially addressed by Schwertfeger et al.,13 and, more recently, the groups of Anderson and Carroll14 and the present inventors' group15 developed drying techniques employing supercritical ethanol that eliminated time consuming solvent exchange steps.
Even with the mitigation of these issues, a processing bottleneck remains, and that is the synthesis of wet gels. Gelation times depend strongly on precursor concentration and pH, and in most cases are on the order of tens of minutes to hours. After gelation, wet gels need to be cured for hours to days to strengthen the silica network.
There is no report on rapid fabrication of mechanically strong aerogels that includes the capability of printing 3D structures.
The present invention seeks to address the problems identified above.